Divide up the phyllo pastry sheets into 2 piles. Beat the eggs in a bowl, add the yoghurt with the baking soda extinguished in it, 3 tbsp oil, the carbonated water and salt to taste.
Take a phyllo pastry sheet, sprinkle it with oil, place a 2nd phyllo pastry sheet on top, sprinkle with oil and crumbled feta. Place another sheet with oil on top, another with feta and so on until you've finished 1 of the piles of sheets.
Roll up the sheets together into a crumbly roll, cut it into 1 1/2″ (3 cm) pieces.
Arrange them next to each other in a buttered oven dish with the cut facing up. Repeat this for the 2nd pile of sheets. Pour the prepared mixture over them with a spoon, place a piece of butter on top of each rose.
Bake in a preheated 356°F (180 °C) oven until golden. Just before they're done baking, take them out and put grated cheese on top of each. Return to the oven for a final 5 min. just to melt the cheese and serve warm!